An elevator power source device may include a speed control unit which receives a power supply from a commercial power source and which can adjust the commercial utility line frequency at will for controlling the speed, and may further include an emergency power supply unit which provides power when the power supply from the commercial power source is stopped, e.g., during power failure. This invention concerns this type of elevator power source device.
FIG. 2 shows a conventional elevator power device of this type. In FIG. 2, a power source monitoring relay 1 is connected to power lines (three-phase, 200/400 V) for providing fixed frequency power from the commercial power source. An AC-DC converter 2 has its input side connected to the commercial power lines and is used for providing DC. A DC-AC inverter 3 has its input side connected to the DC output side of the AC-DC converter 2 and provides AC for controlling an elevator motor 4. A set of batteries 5 is connected to the output side of AC-DC converter 2 via a set of normally closed contacts (which will be closed, i.e., short circuited, during power failure and otherwise open) of power source monitoring relay 1. A battery charger 6 is connected to the power lines via normally open contacts (which will be closed under normal conditions and open circuited during power failure) of power source monitoring relay 1. A DC-AC inverter 7, which, together with a step-up DC reactor (DCL) and a switching unit S connected to it, form an emergency power generating device.
AC reactors ACL are connected to prevent a current surge on the input side of AC-DC converter 2 for controlling the elevator motor and the output side of DC-AC inverter 3. A large-capacitance capacitor C is connected to the input side of DC-AC inverter 3 for controlling the motor. In this way, a voltage source that can guarantee a constant voltage is formed.
The operation is as follows. When the commercial power is supplied, the AC-DC converter 2 supplies DC power to capacitor C on a DC link. The DC link power is converted to AC power with a variable frequency by the DC-AC converter 3. This frequency-variable AC power is supplied to motor 4, which is driven with its speed controlled. For this power supply system, when motor 4 is driven mechanically by the elevator system's counterweight, it can act as a generator with the electrical power generated by it fed back to the power source side. With the power feedback system, the operation efficiency can be improved.
In addition, the commercial power is also used as the power for the elevator control device, and it is used for open/close control of the elevator door, operation of signal device, etc.
In using the commercial electrical power, battery charger 6 always charges battery 5.
During power failure, by a make/break operation of the related contacts NP of power source monitoring relay 1, AC-DC converter 2 and battery charger 6 are cut off from the power lines, and battery 5 is connected via the DC link to the DC-AC inverter 3 for controlling the motor. With the aid of the power supplies from battery 5, the driving of motor 4 is continued until the cage reaches the nearest story. The power from battery 5 is supplied to the elevator control devices via the emergency power generating device, so that there is no break in the control operation.
Although such a conventional elevator power system can certainly operate satisfactorily, it nevertheless uses three sets of converters and inverters. Among them, two sets 2, 7 are not used during normal power supply or in power failure. The design efficiency is therefore poor. This is a cost problem.